A three-dimensional electric field sensor arrangement generally produces an electric field, for example, using a 100 kHz signal. Such an electric field extends vertically more than 10 cm from the device generating the field. A user can enter this field without touching the device, for example with a hand, and gestures performed by a user will disturb the electric field. Such distortions can then be measured and dynamic and static characteristic determined by the arrangement can be used to conclude which type of gesture has been performed.
FIG. 1 shows a typical electrode arrangement 100 that can be used to generate the quasi-static alternating electric near field and to detect disturbances in such a field. The electrode arrangement comprises a non-conductive substrate 130 that allows to arrange a receiving RX electrode 110 above a transmitting TX electrode 120. Here, a printed circuit board 130 may be used wherein the TX electrode 130 covers the entire bottom surface and a strip on the top surface forms one RX electrode 110. However, other arrangements may use multiple RX electrodes and may even employ multiple TX electrodes.
For example, FIG. 2 shows an exemplary arrangement of a printed circuit board 200 wherein a top layer comprises four RX electrodes 210, 220, 230, 240 arranged at the four edges of the printed circuit board 200. Furthermore, a center electrode 250 is arranged within the top layer in the area defined by the four RX electrodes 210, 220, 230, 240. The four RX electrodes 210, 220, 230, 240 may be solid copper strips whereas the center electrode may have a mesh or net structure as shown. The TX electrode as shown in this embodiment may also have mesh structure and may not necessarily be arranged on a bottom layer. As shown in FIG. 3, the printed circuit board 200 may be a multi-layer board and the TX electrode may be arranged in a middle layer and provide for cut out areas to allow placement of RX feeding lines. Moreover, a ground layer may be arranged on the bottom of the printed circuit board for example to provide shielding.
An example of an integrated circuit device that can be connected to such an electrode structure 200 is a gesture evaluation controller MGC3130 also called GestIC® manufactured by Applicant. Achievable range is the most critical factor in electric near field sensing and in GestIC® three-dimensional gesture recognition and tracking technology in particular.